Continuous treatment of metal strip



Aug. 4, 1959 I 1.. VAN ORMER 2,397,693

CONTINUOUS TREATMENT OF METAL STRIP Filed. April 6, 1955 INVENTOR. LAWSON VAN ORMER ATTORNEY CONTINUOUS TREATMENT OF lVIETAL STRIP Lawson Van firmer, Aliquippa, Pa., assignor to Jones 8; Laughlin Steel Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Application April 6, 1955, Serial No. 499,647

4 Claims. (Cl. 80--60) This invention is concerned with the continuous treatment of metal strip. More specifically, it relates to the continuous annealing and temper rolling of low carbon steel strip.

My invention is directed primarily to the preparation of low carbon steel strip for electrotinning but is applicable to strip of other metals and steel strip which is to be used without a coating. The process of my invention will be described with reference to its primary use but it will be understood that this description is not a limitation.

A large proportion of tinplate produced today is made by electrodepositing a coating of tin on a continuous strip of low carbon steel which must be properly prepared for such electrodeposition. conventionally, cold rolled strip is employed as a base metal. The cold rolling operation reduces and elongates the strip very substantially and in so doing hardens the metal and imparts undesirable stifiness thereto. Before electrotinning, therefore, the cold rolled strip is conventionally annealed to relieve the undesirable etfects of cold working. Annealed strip as conventionally produced is softer than is required by most tinplate users and its surface is not such as to produce a desirable appearance when tinned. Therefore, the anhealed strip is slightly reduced in thickness by cold working, usually by rolling while the strip is in tension. That working, which is known as tempering or temper rolling, produces strip having a smooth flat surface and a stiffness greater than annealed strip but, of course, much below that of the cold rolled strip before annealing. The cold working also elongates and hardens the strip somewhat.

The annealing operation above mentioned has been conventionally carried out with the strip in the form of coils. Because of the large mass of steel in a single coil, annealing requires a very extended period of time measured in days, and even so cannot as a practical matter be carried out so as to bring about the desired uniformity of the material from one end of the coil to the other. Alternatively, annealing is sometimes carried out by passing the strip in the form of strand through a continuous annealing furnace, and such method of annealing affords a greater degree of control over the properties of the strip than does coil annealing. It is found, however, that when coil annealed or strand annealed material is temper rolled the product still exhibits non-uniformities from one end of the coil to the other.

It is an object of my invention, therefore, to provide a process of annealing and tempering metal strip so as to produce a product highly uniform in physical properties from one end of the coil to the other. It is another object of my invention to provide a process of annealing and tempering steel strip which makes it possible to produce a uniform product from a starting material which itself is non-uniform over its length. Other objects of my invention will appear in the course of the following description.

I have discovered that if cold rolled, low carbon steel strip is continuously annealed in the form of strand, im-

mediately cold reduced in a temper mill, and the amount of reduction so efiected measured and used to control the conditions in the annealing furnace so that the latter are varied in a manner which compensates for the conditions giving rise to variation in cold reduction, a highly uniform product can be obtained.

The attached drawing is a schematic representation of apparatus arranged to carry out the process of my invention.

Cold rolled strip 1 from a feed reel 5 is passed through a pair of positioning rolls 2. and an electric welder 3, into a pair of pinch rolls 4, which are driven by a motor not shown. The welder 3 is used only to join coils of strip end-to-end. From pinch rolls 4 the strip 1 is passed through cleaning apparatus 6 to remove the cold rolling lubricant and any other foreign matter on the surface, and is conducted into a first looping tower designated generally as 7. That looping tower comprises a series of parallel lower rolls 8 and parallel upper rolls 9 between which the strip is threaded so as to form a series of loops. Upper rolls 9 are mounted on a vertically movable carriage 10 suspended by a cable 12 which passes over sheaves 13 and terminates in a counterweight 15. Looping towers are conventional in the art of continuously treating strip and provide storage means for strip so that the stoppage of the strip either at the entry end of the line for Welding on a new coil or at the exit end of the line for shearing the strip and removing a full coil need not cause the entire line to be shut down. When welder 3, for example, is operating to weld the forward end of a new coil to the trailing end of the coil being processed, strip 1 is paid out from looping tower 7 without stopping since the pull of the strip 1 causes moveable carriage 10 to descend, thus allowing the stored strip to be used.

From looping tower 7 strip 1 passes into a strand annealing furnace designated generally as 17, which may have a heating chamber 18 and a cooling chamber 19. These chambers are provided with a series of parallel bottom rolls 21 and parallel top rolls 22 between which the strip is passed to form a series of loops within the furnace. Heating chamber 18 is provided with heating units 24, which may be electrical resistance heaters, fuel fired -radi ant tube heaters, or other known types. Cooling chamber 19 may be provided with pipe coils 26 through which cooling fluid circulates. A nonoxidizing atmosphere is maintained in chambers 18 and 19 so that the annealed strip is bright and free from scale. The strip 1 passes continuously from heating chamber 18 into cooling chamber 19. From cooling chamber 19 strip 1 passes through a second pair of pinch rolls 17, which are provided with driving motor not shown, and into a second looping tower designated generally 29, which is provided with lower rolls 30, and upper rolls 31 mounted on a movable carriage 32. Carriage 32 is suspended from cable 34 which passes over sheaves 35 and terminates in counteiweight 36. Looping tower 29 operates in the same way as looping tower 7 which has been described. From looping tower 29 the strip 1 passes over a billy roll 38 and through a pair of tension rolls 39, which are provided with motor drive not shown, into the first stand, designated generally 40, of a cold reducing mill. That stand 40 comprises a housing 42, a pair of work rolls 43 and a pair of back-up rolls 4-4. Rolls 43 are driven by electric motor means not shown. Stand 40 is followed by a second stand designated generally 46 which also comprises a housing 47 and a pair of work rolls 48, which are driven by a motor not shown. The strip 1 passes successively through the Work rolls 43 of stand 40 and the rolls 48 of stand 46. Leaving stand 46, it passes through tension rolls 50, which are driven by a motor not shown, and is coiled on tension reel 52.

. 3 The elongation imparted to strip 1 by the cold working in stands 40 and 46 is continuously measured by an elongation gauge designated generally 51. Such gauges,

which areknown to the art, employ a rotatable roll or rolls 54 positioned at the entrance of thecold reducing mill and rolls 55 positioned at the exit end of such mill. These rolls are turned by the strip passing over them and since the strip is elongated somewhat in the cold reducing mill, the exit end rolls 55 turn at a faster speed than the entrance rolls 54. This difference in speed may be used to actuate indicating means 57. An elongation gauge suitable for the method of my invention is described in United States Patents 2,447,268, 2,447,209 and 2,474,116, issued to George H. Rendel and will not be further described here. A control circuit 59, which may be electrical, connects indicating means 57 with heating means 54 of my annealing furnace 17 and control circuit 61 connects indicating means 57 with cooling means 26 of my cooling chamber 19.

I have found that cold rolled strip as supplied to annealing furnaces is, as a practical matter, never uniform from end to end either in chemical composition or physical properties. The non-uniformity with respect to chemical composition probably arises from the fact that it is impossible to produce a steel ingot in which some segregation of chemical constituents does not occur. The nonuniformity in physical properties arises, i believe, from the impossibility of controlling conditions during hot rolling, cooling and cold rolling with the degree of uniformity desired. Because of this initial non-uniformity, I have found it impossible to produce uniform annealed and tempered strip by conventional processes no matter how carefully the annealing and tempering operations are controlled individually. The process of my invention, however, makes it possible to utilize the effects of the tempering operation to control the annealing operation, as will now appear.

Let it be assumed that the strip 1 from coil 5 to be treated by the process of my invention is not entirely uniform from one end of the coil to the other. If such strip were annealed under constant conditions, the resulting product would still exhibit non-uniformities since the annealing practice required to produce the desired product from cold rolled strip having a certain analysis and certain initial hardness cannot produce an identical product from starting material having a different chemical analy-' sis or hardness. In my process the strip 1 is passed through strand annealing furnace 17, which is adjusted to provide a certain cycle of heating and cooling, which wewill assume to be optimum for the strip 1 from the leading end of coil 5. The annealed strip 1 is then immediately passed through temper mill stands 40 and 46 and the elongation of the strip incident to the temper rolling is measured by gauge 51. If, now, the strip half way through coil 5 exhibits an increased hardness, and the conditions in the annealing furnace 17 are not changed, the elongation of this strip in stands 40 and 46 will be somewhat reduced. The reduced elongation will be indicated on indicator 57 and may be used as a guide to readjust conditions within the annealing furnace 17. A decrease in elongation of the strip being tempered indicates that the temperature of annealing furnace 17 should be raised somewhat and, if desired, this alteration can be accomplished automatically through control circuit 59 by means which are conventional and so need not be described. Under certain circumstances it may occur that the change in annealing practice required is most conveniently brought about by decreasing or increasing the temperature of cooling chamber 19 and this may be brought about automatically by control circuit 61 by conventional means which need not be described.

It is thus apparent that the method of my invention makes it possible to adjust annealing conditions for the strip as it passes through the furnace so that the tempermg operation which follows will produce material of a high degree of uniformity from one end of the coil to the other.

The process of my invention is continuous; that is, different portions of strip from the same coil are being annealed and temper rolled at the same time. Because of this, it is generally necessary to cool the annealed strip before it leaves the cooling chamber of the annealing furnace to a lower temperature than would be necessary if the strip were merely coiled at that point. conventionally, steel strip is moved from the annuealing furnace when its temperature falls below that at which it begins to oxidize or scale in air. That temperature is considerably above the temperature at which temper rolling can be properly carried out. i

It will be understood that the measurement of elongation above mentioned is a convenient means of measuring the cold reduction of strip effected by temper rolling and is used herein as a measure of such cold reduction. Direct means of measuring cold reduction such as continuous micrometer means may be used for the same purpose with equal results in my invention.

Although I have mentioned the eifect of annealing and temper rolling upon the properties of hardness, stiffness, reduction in thickness and elongation only of the strip, my invention comprehends the control of other significant properties associated therewith of which the reduction of thickness may be used as an index.

It will also be understood that the process of my invention need not be carried out entirely automatically, although it may be. Gauge 51 may actuate only the indicator 57 and the operator of the line may then adjust conditions within the heating chamber 18 and cooling.

chamber 19 of annealing furnace 17 in accordance with;

the reading of indicator 57 to bring about the desired uniformity of strip.

I claim: 1. The process of treating metal strip in-the form of 'strand comprising continuously annealing said strip, cold Working said strip, thereby reducing its thickness, measuring said reduction of thickness, and varying the annealing in accordance with said measurement to correct for any non-uniformity in reduction of thickness.

2. The process of treating metal strip in the form of strand comprising continuously heating said strip to annealing temperature, cooling said strip to cold working temperature, cold working said strip, thereby elongating it, measuring said elongation, and varying the heating of said strip in accordance with said elongation measurement to correct for any non-uniformity in elongation.

3. The process of treating metal strip in the form of strand comprising continuously heating said strip to annealing temperature, cooling said strip to cold working temperature, cold working said strip, thereby reducing its thickness and increasing its hardness, continuously measuring said reduction of thickness, and varying the cooling of said strip in accordance with said measurement to correct for any non-uniformity in hardness.

4. The process of treating metal strip in the form'of strand comprising continuously passing said strip through an annealing furnace, then immediately through a cold rolling mill, thereby elongating it, continuously measuring said elongation, and varying the temperature in said an nealing furnace in accordance with said elongation measurement to correct for any non-uniformity in elongation.

References Cited in the file of this patent UNITED STATES PATENTS 1,721,350 Naugle July 16, 1929 1,819,764 Blecker Aug. 18, 1931 2,035,312 Greer Mar. 24, 1936 2,154,928 Zuschlag Apr. 18, 1939 2,292,511 Ferm Aug. 11, 1942 2,606,848 Farling Aug. 12, 1952 (Other references on following page) UNITED STATES PATENTS McCaulay Nov. 24, 1953 Dietrich Feb. 9, 1954 Hessenberg June 15, 1954 5 FOREIGN PATENTS Germany May 19, 1930 OTHER REFERENCES Engineering Metallurgy, pages 91-95 by Alexander P. Gwiazdowski, published by C'. C. Nelson Publishing Co. of Appleton, Wis., 1950 ed. 

